feat(particles): bubble trail behind dolphin + block break burst

- BubbleTrail.gd: GPUParticles3D, auto-configured in _ready, set_intensity() API
- BlockBreakParticles.gd: one_shot burst, emit_burst(pos, color) API
- DolphinController.gd: bubble_trail onready + speed_factor hook in _update_movement
- Dolphin.tscn: BubbleEmitterPoint (0,0,1.2) > BubbleTrail child added

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/dolphin/BlockBreakParticles.gd

@@ -0,0 +1,38 @@
+extends GPUParticles3D
+
+func _ready() -> void:
+	amount = 30
+	lifetime = 0.8
+	one_shot = true
+	emitting = false
+	local_coords = false
+
+	var mat := ParticleProcessMaterial.new()
+	mat.direction = Vector3(0.0, 1.0, 0.0)
+	mat.initial_velocity_min = 1.0
+	mat.initial_velocity_max = 3.0
+	mat.spread = 60.0
+	mat.gravity = Vector3(0.0, -2.0, 0.0)
+	mat.scale_min = 0.05
+	mat.scale_max = 0.15
+	process_material = mat
+
+	var box := BoxMesh.new()
+	box.size = Vector3(0.08, 0.08, 0.08)
+
+	var burst_mat := StandardMaterial3D.new()
+	burst_mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
+	burst_mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
+	burst_mat.albedo_color = Color(0.8, 0.7, 0.5, 0.9)
+	box.surface_set_material(0, burst_mat)
+
+	draw_pass_1 = box
+
+
+func emit_burst(pos: Vector3, color: Color) -> void:
+	global_position = pos
+	if draw_pass_1 and draw_pass_1.surface_get_material(0):
+		var mat := draw_pass_1.surface_get_material(0) as StandardMaterial3D
+		if mat:
+			mat.albedo_color = Color(color.r, color.g, color.b, 0.9)
+	emitting = true